Carbon blacks are generally produced in a furnace-type reactor by pyrolyzing a hydrocarbon feedstock with hot combustion gases to produce combustion products containing particulate carbon black.
Carbon blacks may be utilized as pigments, fillers, reinforcing agents and for a variety of other applications. For example, carbon blacks are widely utilized as fillers and reinforcing pigments in the compounding and preparation of rubber compositions.
Carbon blacks for rubber use have a variety of grades depending upon their properties and are generally classified on the basis of analytical properties including: surface area, structure (DBP absorption) and the like. Methods of measuring the surface area of carbon black include an electron microscope, nitrogen surface area (N.sub.2 SA) according to the BET method, CTAB surface area according to the adsorption of cetyltrimethylammonium bromide as a surfactant, and iodine adsorption number (I.sub.2 No.). The structure of a carbon black refers to the linkage of carbon black particles due to agglomeration. As the degree of agglomeration becomes greater, the value of this structure becomes higher.
The properties of the grade of carbon black become an important factor in determining various performances of the rubber composition wherein the carbon blacks are incorporated. Carbon blacks are effective in the preparation of rubber vulcanizates intended for usage in preparing tires. It is generally desirable in the production of tires to utilize carbon blacks which impart high levels of abrasion resistance and low levels of rolling resistance to the tires. The reinforcing properties of a carbon black are generally related to the level of abrasion resistance imparted to the rubber compositions. Generally, carbon blacks with increased reinforcing properties result in tires with increased abrasion resistance.
The grade of the carbon black used mainly for tire treads is classified into HAF (high abrasion furnace), ISAF (intermediate super abrasion furnace) and SAF (super abrasion furnace) with SAF carbon black having a higher surface area than ISAF carbon black which has a higher surface area than HAF carbon black. Abrasion resistance generally improves as surface area increases.
The properties of the grade of carbon black become an important factor in determining various performances of the rubber composition wherein the carbon blacks are incorporated. Generally, carbon blacks having a specific surface area higher than ISAF are used for tire treads of trucks and buses wherein natural rubber is used as a main component. HAF type carbon blacks are generally used for passenger car tire treads wherein synthetic rubbers such as styrene butadiene rubber (SBR) are used as a main component.
Higher surface area carbon blacks impart improved abrasion resistance to tires. However, as specific surface area becomes larger, heat build-up of the rubber compound becomes higher and hysteresis becomes greater. The hysteresis of the compounds means the difference between the energy applied to deform a rubber compound, and the energy released as the rubber compound recovers to its initial undeformed state. Tires with lower hysteresis values have reduced rolling resistance and therefore reduce the fuel consumption of the vehicle utilizing the tire.
Thus it would be desirable to develop a carbon black which would impart both improved abrasion resistance and reduced hysteresis to rubber compounds. Tires prepared with such a carbon black would have lower rolling resistance, to improve the fuel economy of the vehicle utilizing the tire, and improved abrasion resistance, to reduce the tread wear of the tire.
One advantage of the present invention is the production of new carbon blacks which impart increased abrasion resistance and reduced hysteresis properties to natural rubbers, synthetic rubbers and blends of natural and synthetic rubbers incorporating the carbon blacks.
Another object of the present invention is new rubber compositions, advantageous for use as tires, particularly passenger car tires, incorporating the new carbon blacks.
Other objects of the present invention will become apparent from the following description and the claims.